1. Field of the Invention
The present invention relates to a transfer robot. More specifically, the present invention relates to a transfer robot for transporting a thin plate-like work, such as a semiconductor wafer, along a straight path.
2. Description of the Related Art
Among many transfer robots, there is a group of transfer robots which have a mechanism for moving their hands along straight paths (linear transfer mechanism). These robots are simpler in construction and cheaper than the so-called jointed-arm robots, and are used widely in e.g. manufacturing process of semiconductor devices, for transportation of thin, plate-like works such as wafers into and out of different process chambers.
Such transfer robots are disclosed in JP-A-2002-531942 and JP-A-2003-142572, for example. The transfer robots disclosed in these documents generally have a basic construction as shown in FIG. 15 through FIG. 17 of the present application, in which hands 12 are supported via linear transfer mechanisms 11 on a swivel base 10 which is capable of pivoting as well as rising and lowering. More specifically, the transfer robot shown in FIG. 15 through FIG. 17 includes two linear transfer mechanisms 11 of a pivotal arm type. Each linear transfer mechanism 11 is provided with a hand 12 on which a thin, disc-like work W (wafers of silicon, for example) is placed. The two hands 12 supported by respective linear transfer mechanisms 11 overlap each other in plan view, and the two hands 12 are able to move on an identical path in plan view.
Basically, such a transfer robot is required to have a high level of precision for delivering the work W to a predetermined destination as well as for receiving the work W after it is processed. Further, when used in semiconductor manufacturing processes for example, the robot should be operable in a vacuum environment.
The transfer robot shown in FIG. 15 through FIG. 17 of the present application is also operable in the vacuum environment. The hand 12 is provided only with a plurality of regulating members 13 on which the work W can be placed. The regulating members surround the disc-like work W in order to prevent the work from shifting in horizontal directions. This construction is adopted for the hands of the transfer robots disclosed in the above-mentioned Japanese patent application documents. If the hand were provided with e.g. a movable clamp mechanism for enabling operation in the vacuum environment, the wiring and the actuator would become extremely complex in construction, and this would result in high cost and heavy weight for the products.
Such a transfer robot is installed as part of a vacuum transport module which operates between an atmospheric transport module and a plurality of process chambers. As shown in FIG. 18, a vacuum transport module 14 includes for example, a transport chamber 16 surrounded by process chambers 15, an atmospheric transport module 17, and loadlocks 18 connecting the atmospheric transport module 17 and the transport chambers 16 to each other. The transfer robot is placed in the transport chamber 16. The loadlocks 18 have a first door 18a to the atmospheric transport module, and a second door 18b to the transport chamber 16. When the first door 18a is opened and the second door 18b is closed, the inside space of the loadlock 18 becomes atmospheric for movement of works between the atmospheric transport module 17 and the loadlock 18 via the first door 18a. When the first door 18a is closed and the second door 18b is opened, the pressure in the inside space of the loadlock 18 becomes equal to the pressure in the transport chamber 16 (vacuum), for movement of works between the loadlock 18 and the transport chamber 16 via the second door 18b. Each process chamber 15 has a door 15a to the transport chamber 16, and opening the door 15a allows movement of works between the transport chamber 16 and the relevant process chamber 15.
In the vacuum transport module 14, the transfer robot extends the hand 12 to receive a work in the loadlock 18, then retracts the hand 12 into the transport chamber 16, and then turns the swivel base 10 to orient and extend the hand 12 to a desired process chamber 15 to deliver the work to the process chamber 15. Likewise, when receiving a processed work W from the process chambers 15, then transporting them to other process chambers 15 and returning them to the loadlock 18, the transfer robot uses combinations of these extending, retracting and turning operations of the hands 12.
As described above, the transfer robot uses extending, retracting and swiveling movements of the hands 12, with the works W placed thereon. In the above example, however, the works W are surrounded only by the regulating members 13 provided on the hands 12. Thus, in order to prevent the works W from falling off the hands 12 during the transportation, the speed of the hands 12 should be controlled during the operation so as not to become higher than a prescribed level. In particular, much care should be taken in swiveling the hands, since this operation can give rise to a strong centrifugal force. These limitations make it impossible to increase the transfer speed of the robot in moving the works W, thereby leading to a decrease in efficiency of semiconductor production. One idea to prevent the work from falling off during the transfer is to increase the height of the regulating members 13 of the hands 12. However, such an increase makes it necessary to increase raising-lowering stroke of the swivel base 10 or of the hands 12 for loading and unloading the works W. Further, if the two hands move on two respective paths which are identical as in plan view but spaced vertically as shown in FIG. 17, the two hands 12 must be spaced widely from each other. Unfavorably this leads to an increase in the raising-lowering stroke of the swivel base 10, and also to an increase in weight of the hands 12.